Friction material



United States Patent Jersey No Drawing. Filed Jan. 2, 1962, Ser. No.163,871

Claims. ((11. 752il6) This invention relates to the production offriction material, and particularly to friction material composed inmajor amount by volume of metal.

More particularly, it is an object of the present invention to providefriction material characterized by its high heat resistant, porous,sintered metal content, making it particularly suitable for hightemperature application, such as for industrial, truck, bus, andaircraft clutch or brake elements where high frictional heat isgenerated.

It is a further object of the present invention to provide a frictionelement of the character a foresaid composed, in minor amount by volume,of a ceramic friction material such as alumina or magnesia dispersed ina continuous phase or matrix composed of high melting point metal inmajor amount by volume.

The term high melting point metal as employed herein is understood tomean sinterable metals having melting points of over 2500 R, such asiron, nickel, molybdenum, tungsten, chromium, vanadium, tantalum, boronand columbium, some of which metals, and their combinations or alloys,permit production products having melting points in excess of 4000 F.

Although the process of the present invention employs generallyconventional sintering technique, comprising first the formation ofmolded compacts of powdered compositions followed by disposing thecompacts in stacks in an externally heated oven to accomplish sintering,it permits the sintering of metals which are not generally amenable tosintering in such manner.

Such sintering is accomplished herein by combining, in the compactedpowder composition, ingredients that react exothermically to producelocalized wafer temperatures sufiicient for sintering, and which areignited under conventional sintering temperatures, such as from about1400 F. to about 1800 F.

The aforesaid reaction comprises a heat initiated exothermic reactionbetween, for example, aluminum and an oxide of high melting metal suchas for example molybdenum trioxide, to form the ceramic frictionmaterial aluminum oxide and metallic molybdenum.

It has been unexpectedly found, in accordance with the presentinvention, that by addition of powdered metallic additives to theforegoing composition in the mixture from which the compact is formed,and in an amount sufficient to provide the final sintered product with ametal content of from at least 50% and up to about 75% by volume, thatcontrol of the normally rapid high temperature exothermic reaction isobtained. This also results in elimination of fissures and cracksresulting from volume and temperature changes and permits use of aprecompacted wafer necessary in preparing friction material by generallyconventional sintering technique.

This process or reaction tempering metal additive can be selected fordesirable properties in the final product. Thus, nickel added to thefollowing reaction, for example, MoO +2Al Al O +Mo, will alloy with themolybdenum to provide an oxidation resistant compound, avoiding hightemperature catastrophic oxidation associated with unalloyed molybdenum.Similarly, chromium addition to the above reaction will result in amolybdenum-chromium alloy of exceptional value in resistance to thermalshock.

Further, the metallic additive can be selected for other desirable endresults. Cobalt, for example, added to the Bidifififi Patented May 18,1965 reaction: WO +2Al Al O +W, besides providing a desirable alloy forparticular applications, seems to act as a flux aiding the sinteringoperation. Without the controlling or moderating additive metal thetungsten would melt and the alumina would segregate. With this diluentmetal the reaction slows down and forms a uniform sintered composition.

Production of the products of the present invention comprises mixing inpowdered form metallic aluminum or magnesium together with asubstantially stoichiometric amount of an oxide of high melting pointmetal, which will be reduced to the metal in the subsequent reactionwherein the first mentioned metals become converted to their refractoryoxides. To these is added at least one other high melting point powderedmetal additive which does not become oxidized in the reaction, in anamount to provide the final product with a total high melting pointmetal content of at least by volume, as aforesaid. The particle size ofthe foregoing powders is in part determined by the desired reactionrate, but also lies within conventional ranges to avoid segregation inhandling and molding. Distribution between 200 mesh size to 5 micronshas been found most advantageous.

The mixed powders are compacted in the cold by molding in confinedshaped molds at pressures of from about 5 to about 50 tons per sqaureinch, to form disc, ring, or other shaped compacts of controlleddensity, such density also being a factor in the subsequent reactionrate. These molded compacts are then ignited to initiate the subsequentself-sustaining high temperature oxidation-reduction reaction bydisposoing them in stacks in sintering furnaces of the direct flame, gasand electric sintering or induction heating types.

It has been found advantageous to apply pressure to the compacts duringthe ignition operation, and this has been most readily accomplished inequipment designer; for standard sintered products. Relatively lowpressure, such as on the order of 100-250 pounds per square inch hasbeen found satisfactory, since pressure at maximum temperature isassured. This pressure during heating and ignition has a twofoldpurpose, the first being to obtain desired final product density. Forexample, the percentage values after the following reactions are thetheoretical volume change in the described chemical reaction:

Percent 3V O -]-10Al 5Al O +6V 28 Cr O +2Al Al O +2Cr 13MOO3+ZAI9AIZO3+MO The applied pressure during this stage thus serves toovercome low density material resulting from such volume shrinkage.

The second benefit of pressure during the heating and igniting stage inthe sintering furnace is the ability to therein bond the sinteredproduct to a backing plate or steel core. Pressure applied at the timeof ignition insures good contact at elevated temperature most necessaryfor satisfactory bond.

Since the powdered mix is employed in compacted form, and the period ofignition can be relatively short, protective atmosphere is not criticalin many cases. However, when a metal such as aluminum or magnesium isused to reduce a metallic oxide, any oxygen present will readily reactwith the available surface metal to produce weak, powdery edges. Thiscan be avoided by the use of a protective atmosphere such as carbonmonoxide.

Ignition temperature is, of course, a function of the reactants and canreadily be determined for each individual mixture. Reduction of ametallic oxide by aluminum will, in most cases, proceed under 1800 F.

The following examples are for the purpose of illuss e race 3 tration,but many modifications will be obvious to fulfill specific requirements.

Example I 25 parts by weight of a stoichiometric amount of powderedaluminum and molybdic oxide was mixed with 75 parts by weight ofnickelpowder, molded to the shape of a friction disc at 10 t.s.i., andsintered at 1400 F. under a pressure of100 p.s.i..in a furnace. Aprotective atmosphere of unpurified exothermic gas was employed. Thefinal product, having the cpmposition Percent (by volume) A1 32 Mo 8 Ni60 presented a bright metallic appearance and good strength. Asatisfactory bond of the disc to an unplated, wheel abradedsteel-backing plate Was obtained. This material used as frictionmaterial element in a brake satisfactorily absorbed 1200 ft.-lbs./ in.sec. at temperatures well above Example II A powdered compact of thecomposition Percent weight V 0 16 A1 8 Mo 74 was ignited by direct flamein a sintering furnace under a pressure of 250 p.s.i. to give a finalcomposition:

Percent volume A1 0 3 1 V 12 Mo 5 7 Similarly, this reaction has beenused to sinter tungsten.

Example 111 Other reactions tested are indicated below together withmetallic additives that have been used in preparing sintered metalfriction elements in the method previously described:

Additives: Mo, Cr, Ni, Fe, Fe/B.

CO2O3|-2A1- A12O3+2CO Additives: Cr.

Additives: Fe.

I claim:

1. The method of making a high heat resistant, sintered, porous,.friction material composition which comprises, mixing (A) apowderedmetal selected from the group consisting of aluminum andmagnesium with (B) asub- .stantia'lly stoichiometric amount-of an oxideof a high melting point metal, and (C) a powdered high melting pointmetal, cold compacting this mix with pressure to form a handleableshaped compact, then .heatingthis shaped compact to initiate anexothermic reaction .whereby said first metal (A) is converted to itsrefractory. oxide and said oxide (B) is reduced to its free metal, saidhigh melting point additive (C) alloyingwith. saidfree-metal and beingin an amountto provideia total free metalcontinuous matrix in theproportion of from at. least 50% to about by total volume, with saidresulting refractory oxide being substantially uniformly dispersedtherein.

2. The process of claim 1 wherein the first powdered metal is aluminum.

3. The process of .claim 1 .wherein said powders are compacted in ashaped mold at a pressure of from. about 5 to about 50 tons .per squareinch.

4. The process of claim 1 wherein said powdered'compact is ignited undercompacting. pressure in a sinterin furnace.

5. The process of claim 1 wherein said powdered compact is ignited undercompacting pressure in contact with a solid metal backing plate andunited therewith by an in situ formed sintered bond.

References Cited by the Examiner UNITED STATES PATENTS 2,848,324 8/58Kropf 75-120 2,936,250 5/60 Glaser 29182.5 2,973,570 3/61 Nochtman29182.5 3,010,825 11/61 Michandet al. 75-206 3,019,103 '1/62 Alexanderet a1. 75 206 3,024,110 3/62 Fun'xhouser et a1 75-206 3,034,200 5/62Tragert 29'1-82.5 3,045,332 7/62 Denison 29-1825 CARL D. QUARFORTH,Primary Examiner.

REUBEN EPSTEIN, OSCAR R. VERTILExaminers.

1. THE METHOD OF MAKING A HIGH HEAT RESISTANT, SINTERED, POROUS,FRICTION MATERIAL COMPOSITION WHICH COMPRISES, MIXING (A) A POWDEREDMETAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM AND MAGNESIUM WITH(B) A SUBSTANTIALLY STOICHIOMETRIC AMOUNT OF AN OXIDE OF A HIGH MELTINGPOING METAL, AND (C) A POWDERED HIGH MELTING POINT METAL, COLDCOMPACTING THIS MIX WITH PRESSURE TO FORM A HANDLEABLE SHAPED COMPACT,THEN HEATING THIS SHAPED COMPACT TO INITIATE AN EXOTHERMIC REACTIONWHEREBY SAID FIRST METAL (A) IS CONVERTED TO ITS REFRACTORY OXIDE ANDSAID OXIDE (B) IS REDUCED TO ITS FREE METAL, SAID HIGH MELTING POINGADDITIVE (C) ALLOYING WITH SAID FREE METAL AND BEING IN AN AMOUNT TOPROVIDE A TOTAL FREE MAETAL CONTINUOUS MATRIX IN THE PROPORTION OF FROMAT LEAST 50% TO ABOUT 75% BY TOTAL VOLUME, WITH SAID RESULTINGREFRACTORY OXIDE BEING SUBSTANTIALLY UNIFORMLY DISPERSED THEREIN.